1. Field of the Invention
The present invention relates to a method of fabricating a spherical quantum dot device by a combination of gas condensation and an epitaxial technique.
2. Description of the Prior Art
Quantum dot (QD) structures have already been used extensively in Laser Diodes (LD), Light-Emitting Diodes (LED), and infrared detectors (QDIP), and are now replacing traditional quantum well structure gradually. Although the quantum well infrared detector has shown good performance nowadays, the property of a forbidden normal incidence must be overcome in order to fabricate the detector arrays. A quantum dot infrared detector has been developed because it has several advantages such as high normal incidence absorption, high operation temperature, and so on. Molecular Beam Epitaxy (MBE) and Metal Organic Chemical Vapor Deposition (MOCVD) are employed for growing quantum dots and the stress resulted from the lattice mismatch between a substrate and an epilayer so as to form quantum dots. Besides, there are other methods that can also form quantum dots, such as chemical synthesis and gas condensation. Gas condensation can be achieved by a thermal evaporation method, a sputtering method, an e-beam evaporation method, a laser ablation method and so on. However, in the epitaxial techniques such as MBE and MOCVD, the grown quantum dots cannot be formed with a complete spherical-like structure and the ability of an infrared detector to absorb normal incidence radiation is deficient.
A primary objective of the present invention is to provide a method of fabricating a device with spherical quantum dots device by a combination of gas condensation and an epitaxial technique. The present invention can improve the structure of spherical quantum dots so as to achieve a three-dimensional quantum confinement effect, and can improve the ability to absorb normal incidence absorption radiation so as to reduce the cost of fabricating detector arrays.
Another objective of the present invention is to provide a method of fabricating a multi-layer quantum dots device. By repeating the method of fabricating the spherical quantum dots device, the multi-layer quantum dots device with excellent quality can be achieved by a combination of gas condensation and an epitaxial technique.
To achieve the above and other objectives, a method of fabricating a spherical quantum dot device by a combination of gas condensation and an epitaxial technique comprises the following steps:
a. A quantum dots growth step, when quantum dots are grown on a substrate by gas condensation method.
b. A quantum dots process processing step, when an ultrasonic cleaner is used with an organic solvent to vibrate the substrate in which quantum dots have been grown in step (a) or the substrate is thermally annealed to high temperature in which quantum dots have been grown thereon in step (a);
c. An epitaxial layer cover step, when the epitaxial technique is used for covering an epitaxial layer on the quantum dots sample which has been processed by step (b).
By virtue of the above-mentioned steps, a device with completely spherical quantum dots can be fabricated and the faults of the foregoing epitaxial growth technique, which cannot form complete spherical quantum dots, can be overcome.
Moreover, the present invention further comprises a substrate process step, wherein a reactive ion etching method is used to process the substrate and make the surface of the substrate rough so as to increase the growth density of quantum dots in the quantum dots growth step.